Present laptop, palmtop or other type of portable battery powered computers include miniature disk drive units which can be subjected to extreme shocks, for example when such a computer is dropped during normal use. In some cases, severe damage may occur to the computer.
The hard disk drive of a computer is especially vulnerable to impact because the proper operation of the drive is dependent on the maintenance of a very small gap between the drive heads and the disk. In the event that the heads were to contact the disk upon a shock to the computer, the heads could be damaged, and perhaps even more serious, magnetic material containing data could be damaged. This phenomenon, known as "head crash", can irretrievably destroy data.
Thus it is important to prevent contact between the heads and disk upon impact, so that valuable data stored on the disk is preserved.
Typical prior art methods of protection rely on reaction to the shock to the portable computer after it occurs (see, for example, U.S. Pat. No. 5,235,472 to Smith and U.S. Pat. No. 4,862,298 to Genheimer et al.). These methods rely on the heads being parked either on a data-free landing zone or unloaded from the disk surface, it being understood that in general the disk drive can tolerate greater shock with the heads parked than when the heads are in a loaded state. Clearly superior to this is an approach which is predictive, using data for protecting the disk drive prior to impact of the computer.
U.S. Pat. No. 5,227,929 to Comerford proposes such a system which includes a three axis accelerometer and a dedicated microprocessor which interrupts the computer CPU so that the CPU can exercise a program to communicate with the disk drive which in turn commands the heads of the disk drive to retract. This series of events takes a relatively long time, which in fact may be so long that the computer may be subject to impact prior to the heads being retracted. Furthermore, the combination of a three axis accelerometer and a dedicated microprocessor is a complex and expensive proposed solution. In addition, operation is dependent on the control microprocessor taking action and the disk drive responding in time to prevent damage.
It would be highly advantageous to provide a low cost method of predicting shocks that can be implemented within the disk drive unit and which utilizes the embedded disk drive control microprocessor so as to avoid unpredictable delays and host computers system and software dependencies.